Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended							9 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Numerator:
Net income (loss) attributable to Acadia Healthcare Company, Inc.	$ 68,132	$ 78,482	$ 76,383	$ 57,729	$ (217,710)	$ 72,299	$ 66,015	$ 222,997	$ (79,396)
Denominator:
Weighted average shares outstanding for basic earnings per share	91,720				91,168			91,571	90,852
Effects of dilutive instruments	468				0			548	0
Shares used in computing diluted earnings per common share	92,188				91,168			92,119	90,852
Basic earnings (loss) per share attributable to Acadia Healthcare Company, Inc. stockholders:
Basic	$ 0.74				$ (2.39)			$ 2.44	$ (0.87)
Diluted earnings (loss) per share attributable to Acadia Healthcare Company, Inc. stockholders:
Diluted	$ 0.74				$ (2.39)			$ 2.42	$ (0.87)